Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$129.39	12.591%	$145.6815	$145.68	$145.70	$145.70
Purchase #2	$125.90	8.405%	$136.4819	$136.48	$136.50	$136.50
Purchase #3	$201.99	6.575%	$215.2708	$215.27	$215.25	$215.30
Purchase #4	$48.28	10.657%	$53.4252	$53.43	$53.45	$53.40
Purchase #5	$38.69	13.665%	$43.977	$43.98	$44.00	$44.00
Purchase #6	$168.61	13.611%	$191.5595	$191.56	$191.55	$191.60
Purchase #7	$172.73	7.161%	$185.0992	$185.10	$185.10	$185.10
7 purchase totals =	$885.59		$971.4951	$971.50	$971.55	$971.60